MicroRNAs (miRNA) are a recently discovered class of small non-coding RNAs (17-14 nucleotides). Due to their function as regulators of gene expression they play a critical role both in physiological and in pathological processes, such as cancer (Calin and Croce 2006; Esquela-Kerscher and Slack 2006; Zhang, Pan et al. 2007; Sassen, Miska et al. 2008).
There is increasing evidence that miRNAs are not only found in tissues but also in human blood both as free circulating nucleic acids (also called circulating miRNAs) and in mononuclear cells. A recent proof-of-principle study demonstrated miRNA expression pattern in pooled blood sera and pooled blood cells, both in healthy individuals and in cancer patients including patients with lung cancer (Chen, Ba et al. 2008). In addition, a remarkable stability of miRNAs in human sera was recently demonstrated (Chen, Ba et al. 2008; Gilad, Meiri et al. 2008). These findings make miRNA a potential tool for diagnostics for various types of diseases based on blood analysis.
Multiple sclerosis (MS), also known as disseminated sclerosis or encephalomyelitis disseminata) is an inflammatory autoimmune disease of the central nervous system (CNS). Causing MS appears to be a combination of immunological, genetic and environmental factors. It is a chronic demyelinating disease, which primarily affects young adults and is characterized by a highly variable course. The heterogeneous presentation of MS is characterized by a variety of clinical problems arising from multiple regions of demyelination and inflammation along axonal pathways. The signs and symptoms of MS are determined by the location of the affected regions.
Mostly, the disease begins in the third or fourth decade of life. Its initial course is characterized by acute episodes of neurological dysfunction, such as decreased vision, followed by subsequent recovery. This course is known as relapsing-remitting MS. Over time, the improvement after attacks may be incomplete and the relapsing-remitting course may evolve into one of increasing progression of disability, termed secondary progressive MS.
The diagnosis of MS generally relies on the presence of a neurological problem that remits and then returns at an unrelated site. This is confirmed by magnetic resonance imaging (MRI) or functional evidence of lesions in a particular pathway by abnormal evoked potentials. The histological hallmark of MS at postmortem exam is multiple lesions at different sites showing loss of myelin and infiltration by a characteristic complement of inflammatory cells.
The key to identifying predictive markers is a deeper understanding of the factors that underlie the therapeutic response. Identification of biomarkers will in turn allow for stratification of MS patients for their response to a specific treatment, ultimately leading to improved therapeutic benefits and a personalized treatment approach for MS patients.
Identification of reliable biomarkers in MS sclerosis patients bears the potential for an improved MS diagnosis, monitoring the disease activity and progression and also to evaluate response to treatments. The field of biomarker discovery has gradually shifted from the aim to find the perfect surrogate marker to the construction of composite markers with higher performances, taking advantage of technologies allowing unbiased screening, including microarray analyses. However, suitable biomarker sets allowing for a non-invasive diagnosis of MS based on peripheral profiles have not been detected, so far.
Various markers have been proposed to indicate specific types of disorders such as cancer or MS. However, there is still a need for more efficient and effective methods and compositions for the diagnosis of diseases.